From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756470Ab3CENbE (ORCPT ); Tue, 5 Mar 2013 08:31:04 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:54543 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756186Ab3CENbB (ORCPT ); Tue, 5 Mar 2013 08:31:01 -0500 Message-ID: <1362490253.4392.159.camel@falcor1> Subject: Re: [PATCH 2/6] ima: Return INTEGRITY_FAIL if digital signature can't be verified From: Mimi Zohar To: Vivek Goyal Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, dmitry.kasatkin@intel.com Date: Tue, 05 Mar 2013 08:30:53 -0500 In-Reply-To: <20130304162033.GB15199@redhat.com> References: <1360871745-20616-1-git-send-email-vgoyal@redhat.com> <1360871745-20616-3-git-send-email-vgoyal@redhat.com> <1362404916.4392.25.camel@falcor1> <20130304162033.GB15199@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 (3.2.3-3.fc16) Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13030513-3620-0000-0000-0000017AA836 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2013-03-04 at 11:20 -0500, Vivek Goyal wrote: > On Mon, Mar 04, 2013 at 08:48:36AM -0500, Mimi Zohar wrote: > > On Thu, 2013-02-14 at 14:55 -0500, Vivek Goyal wrote: > > > Digital signature verification happens using integrity_digsig_verify(). > > > Curently we set integrity to FAIL for all error codes except -EOPNOTSUPP. > > > This sounds out of line. > > > > > > - If appropriate kernel code is not compiled in to verify signature of > > > a file, then prractically it is a failed signature. > > > > > > - For so many other possible errors we are setting the status to fail. > > > For example, -EINVAL, -ENOKEY, -ENOMEM, -EINVAL, -ENOTSUPP etc, it > > > beats me that why -EOPNOTSUPP is special. > > > > > > This patch should make the semantics more consistent. That is, if digital > > > signature is present in security.ima, then any error happened during > > > signature processing leads to status INTEGRITY_FAIL. > > > > > > AFAICS, it should not have any user visible effect on existing > > > application. In some cases we will start returning INTEGRITY_FAIL > > > instead of INTEGRITY_UNKNOWN. And process_measurement() will deny access > > > to file both in case of INTEGRITY_UNKNOWN and INTEGRITY_FAIL. > > > > > > Signed-off-by: Vivek Goyal > > > > A number of patches in this patchset more finely differentiate return > > codes, which is good. I agree with you totally that there is no good > > reason for -EOPNOTSUPP to be handled differently. Unfortunately, the > > initramfs is CPIO, which doesn't support xattrs. With the proposed > > change and 'ima_appraise_tcb' flag enabled, we wouldn't be able to boot. > > I really dislike hard coding policy in the kernel. > > Hi Mimi, > > If there are no xattr, then we will not even hit this code. We will > bail out early in vfs_getxattr_alloc(). > > I thought that one of the DON_APPRAISE rules will kick in for initramfs > and files in initramfs will not be appraised and boot will continue. > > {.action = DONT_APPRAISE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC}, > {.action = DONT_APPRAISE,.fsmagic = RAMFS_MAGIC,.flags = IMA_FSMAGIC}, > > Is that not the case here? Right, thanks for the clarification. Perhaps we could abbreviate the patch description like: Digital signature verification happens using integrity_digsig_verify(). If a digital signature is present in security.ima, then any error, which happens during signature verification, should lead to status INTEGRITY_FAIL. In the future we might want to differentiate between persistent (eg. -ENOMEM) vs. non-persistent errors, in order to cache failures. This patch removes the unnecessary -EOPNOTSUPP test. thanks, Mimi